Plastic container

ABSTRACT

A plastic for container manufacture comprising at least 90 percent of an interpolymer of 60 to 70 percent by weight of vinylidene chloride and 40 to 30 percent by weight of butadiene having an improved combination of important and critical properties.

Unite States Pater [191 Pinsky et a1.

[ Oct. 22, 1974 US. Cl 260/890, 260/821, 260/877, 204/159.22, 215/1 C Int. Cl. C08f 29/22, C08f 15/08 Field of Search 260/821, 87.7, 890; 215/1 C References Cited UNITED STATES PATENTS 10/1948 Stephenson 18/47.5

2,624,724 1/1953 Park 260/928 3,137,681 6/1964 Orr 260/821 3,165,491 1/1965 Butzler et a1. 260/318 3,477,999 11/1969 Takeda et al. 260/785 Primary ExaminerJoseph L. Schofer Assistant Examiner-William F. Hamrock Attorney, Agent, or Firm-Michael .1. Murphy A plastic for container manufacture comprising at least 90 percent of an interpolymer of 60 to 70 percent by weight of vinylidene chloride and 40 to 30 percent by weight of butadiene having an improved combination of important and critical properties.

ABSTRACT 1 Claim, No Drawings This invention relates to an improved plastic for manufacturing containers designed to package foods, beverages and other products and in particular to a container composed of a specific interpolymer composition having an improved combination of important and critical properties required for the packaging of comestibles and other products.

Many different types of plastic material are currently being employed in containers used for packaging prod ucts such as foods, beverages, cosmetics and the like. in general, a particular plastic which is used to package a product such as a perishable food is selected because of one or a very few outstanding properties of the plastic which appear to outweigh other important property requirements which may be deficient in the same plastic. Unfortunately, these property deficiencies have tended to limit the usefulness of plastic materials to fulfill many packaging needs and as the emphasis has increased to improve product quality and shelf-life, these deficiencies have become even more of a concern as limiting factors. Consequently, the need to develop plastic materials having an improved range of properties has become extremely important to the plastic container industry. Now. an interpolymer of vinylidene chlorine and butadiene has been developed having properties considered necessary for the packaging of those products such as foods which can be affected by the type of material used to construct the container. Interpolymers of vinylidene and butadiene are broadly known to have desirable barrier properties but unfortunately these same interpolymers have not been considered practical for general container usage because of deficiencies in several critical property requirements such as its tendencyto absorb or transfer product ingredients, stiffness, capability to withstand steam sterilization andthe like. Now it has been found that an interpolymer of vinylidene chloride and butadiene can be created having a broad combination of property characteristics considered essential for the packaging of products such as referred to above.

The primary object of this invention is to provide a plastic material having an improved combination of properties considered important for packaging purposes.

It is a further object of this invention to provide a plastic container having an improved combination of properties considered important for packaging envi- 'ronmentally sensitive products.

it is another object of this invention to provide an improved plastic material composed primarily of chemically combined vinylidene chloride and butadiene.

it is a further objectof this invention to provide an improved plastic container composed of at least 90 percent of an interpolymer of vinylidene chloride and butadiene in certain critical proportions.

Other objects of this invention will in part be obvious and will in part appear hereinafter.

These and other objects are attained by a plastic container comprising at least 90 percent of a chemically combined interpolymer of 60 to 70 percent by weight of vinylidene chloride and 40 to 30 percent by weight of butadiene.

The following examples are given to set forth and illustrate more clearly the principle and'practice of this '2 invention. Unless otherwise specified, parts or quantities are mentioned on a weight basis.

EXAMPLE I The following is charged to apressure vessel equipped with an agitator, temperature controlling means and an inlet to be used during operation of the vessel:

Parts Water i500 Butadiene Monomer 370 Sodium Lauryl Sulfate 3.0 0.7

Potassium Persulfute Polymerizationis carried out while agitating under atmospheric pressure at 30C. by gradually adding 630 parts vinylidene chloride monomer at a constant rate over about a twelve-hour period. Towards the end of the addition cycle, the polymer is sampled and tested interpolymer having a molecular weight of about 100,000 Staudinger.

500 Parts of the resin thus obtained are blended with 10 parts epoxidized soya bean oil (lubricant) and 15 parts calcium. zinc (stabilizer) and the resulting blend is fed to a conventional pilot plant. type blow molding extruder which in this case is a single barrel extruder with a 3 foot long, inch diameter screw, connected at its discharge end to a downwardly facing die having an 0.20 inch wide annular orifice of 1% inch diameter. Continuous extrusion is maintained at'a barrel temper ature of approximately 500F. to extrude a tubular parison of 0.19 inch wall thickness downwardly between opposing mold halves configured to produce a plastic bottle after blowing having a cylindrical 2 inch diameter body extending 4% inch in length with a closed substantially flat bottom on one end and a shoulder on the other end uniformly tapering inwardlyto a inch diameter by /2 inch long open externally threaded neck. To manufacture a bottle the mold halves are brought together and closed around a portion of the downwardly. advancing extruded parison and the parison severed immediately above the mold after which a blowing needle is inserted into the upper end of the parison held by the mold toblow the bottle into the configuration described above. The mold is cooled and the mold halves separated to discharge a plastic bottle of approximately 0.030 inch average body, wall thickness which is somewhat thicker atits neck portion. The molding operation is repeated while continuously extruding until sufficient bottles are produced to carry out all of the tests described below some of which are run on the bottle and some of which are run on a flattened sample, obtained by severing the bottom and shoulder portion from the bottle to obtain a 4 inch long cylindrical section which is out once longitudinally and opened into an approximately 4 X 6 inch plastic sample. The samples, either bottle or 4 X 6 inch flattened section, are

subjected to the following tests and the results tabulated in Table I.

l. Polymer Processability this property involves the capability of a polymer to-be melt processed and extruded through an orifice or die and subsequently formed into a structurally sound container. The polymer must blow smoothly and remain thermoplastic throughout and after processing so that scrap material may be reprocessed. Bottles obtained by the abovedescribed blow molding procedure should be substantially rigid, conform closely to the mold cavity configuration and have relatively uniform wall thickness throughout with no significant localized weaknesses. More specifically, any polymer which does not (l) upon extrusion, flow smoothly to produce a relatively even tubular parison, (2) after parison formation, be expandable laterally and uniformly with respect to material distribution at least three fold, and (3) after expansion, be thermoplastic throughout (no localized weaknesses) is not considered acceptable. To determine reprocessability, several of the bottles are ground into small particles and again reprocessed through the extruder to form bottles in the same manner as described above. The reformed bottles should conform substantially to. the bottles which were originally ground.

2. Oxygen Permeability the oxygen permeability test is run on the flattened sample according to ASTM D- 1434-58. More specifically, a 3 inch diameter disc is severed from the 4 X 6 inch sample and clamped around its outer margin within a permeability cell such that the chamber within the cell is divided by the sample into two chamber portions which have been evacuated of all residual gases and vapors. One of these chamber portions is .filled with an atmosphere (760 mm Hg.) of pure, dry oxygen and the chamber portion on the opposite side of the disc is maintained under vacuum. After 24 hours under these conditions at a temperature of 7-3'F., the amount of oxygen passing through the disc is measured (by pressure) and the oxygen permeability rate is calculated in terms of cc/day/ l sq.in./mil-atmosphere at 73F.

3. Water Permeability the water permeability test is run on the bottle and is measured by filling the bottle I substantially full with water at 73F. and capping the bottle witha moisture impermeable closure. The filled bottle is then weighed and placed in an air tight chamber containing an atmosphere of circulating air at 50 percent relative humidity and 73F. After 28 days under conditions, the amount of water lost by the bottle is measured by reweighing the bottle and the permeability is calculated in terms of gram/day/IOO sq.in./mil at 73F. (50 percent RH).

4. Toughness this property is measured by filling I several bottles with water approximately 1 inch from the top edge of the neck, capping the bottle securely with an air tight closure and then dropping the bottles from various heights. The Estimated Mean Failure Height (EMFH) is determined to be that height at which 50 percent of the bottles break. This test is more commonly known as the Bruceton Staircase Method.

5. Product Absorption this property is defined as the container plastics capability to be non-absorbing with respect to the products packaged within the container and is measured by filling a bottle with a O.l percent solution of peppermint oil in a 75/25 water/alcohol mixture and maintaining the bottle and contents for 30 days at a temperature of 120F. After this interval, the loss of peppermint oil from the solution is measured by gas chromatography.

6. Water Vapor Permeability water vapor permeability of the plastic is the capability of the plastic to transfer moisture from the vapor state through the plastic and is measured according to the method outlined in ASTM E-96-63T. Briefly, a bottle is filled with calcium chloride desiccant, sealed with a moisture impermeable closure and weighed. The sealed bottle is then placed in a chamber containing an atmosphere of circulating air at percent relative humidity and 100F. for 28 days after which the bottle and contents are reweighed. The results are used to calculate the Water Vapor Transmission Rate (WVTR) in terms of grams/day/lOO sq.in./mil at l00F. (95 percent RH).

7. Stijjness the stiffness of the plastic is run on the flattened sample of the bottle and is measured by calculating the stiffness modulus of the sample as described in ASTM D-747-63.

8. Heat Distortion Temperature the Heat Distortion Temperature test is run on the flattened sample obtained from the bottle and is measured by the procedure described in ASTM D-l637-61.

9. Product Ingredient Impermeability the bottle of the present invention should be capable of containing a variety of product ingredients for long periods of time without significant loss of any one or more of the ingredients of the product from the bottle. Asa general measure of Product Ingredient lmpermeability, two' tests have been developed and are described as follows:

a. Polar Liquid Permeability in this test the bottle is filled to 80 percent capacity with pure ethyl acetate liquid. The filled bottle is sealed, weighed and placed in the chamber containing an atmosphere of circulating air at 50 percent relative humidity and 73F. and maintained under these conditions for 28 days after which the bottle is reweighed to determine the weight loss which is in turn used to calculate the permeation rate of ethyl acetate in terms of grams/day/ 100 sq. in./mil at 73F. (50 percent RH).

b. Non-polar Liquid Permeability the measure of the capability of the plastic to act as a barrier against non polar liquids such as hydrocarbon liquids is measured by filling the bottle to 80 percent capacity with pure hexane after which the bottle is sealed, weighed and placed in a chamber containing an atmosphere of circulating air at 50 percent relative humidity and 73F. The bottle is maintained under these conditions for 28 days after which the bottle is reweighed to determine the weight loss which is used to calculate the permeation rate of hexane in terms of grams/day/ I00 sq.in./mil at 73F. (50 percent RH).

10. Densitythe density of the plastic is measured from the flattened sample in accordance with ASTM D-l895-61T and calculated in terms of grams/cc at 73F.

11. Steam Sterilizability steam sterilizability is the bottles capability to be steam autoclaved after a food product has been packaged in the bottle. This test is carried out by subjecting a sealed bottle containing the product to 270F. steam under pressure (250 psi) for 30 minutes. Under these conditions there should be no permanent changes in the basic bottle configuration or product. To be acceptable, the bottle should show no significant distortion or discoloration.

' EXAMPLE [1 The procedure of Example 1 is repeated except that 320 parts of butadiene monomer and 680 parts of vinylidene chloride monomer are added to the reactor instead of the 370 butadiene monomer/630 parts vinylidene chloride monomer used in Example 1 and the polymerization is allowed to proceed until a copolymer of 68:32 vinylidene chloridezbutadiene is obtained. The test results which are obtained are tabulated in Table 1.

EXAMPLE Ill The procedure of Example I is repeated except that 450 parts of butadiene monomer and 555 parts of vinylidene chloride monomer are added to the reactor instead of the 370 butadiene monomer/630 parts vinylidene chloride monomer used in Example I and the po lymerization is allowed to proceed until a copolymer of 55:45 vinylidene chloridezbutadiene is obtained. The

test results which are'obtained are tabulated in Table v EXAMPLE IV The procedure of Example I is repeated except that 150 parts of butadiene monomer and 850 parts of vinylidene chloride monomer are added to the reactor instead of the 370 butadiene monomer/630 parts vinylidene chloride monomer used in Example 1 and the polymerization is allowed to proceed untila copolymer of EXAMPLE V The procedure of Example 1 is repeated except that 600 parts of butadiene monomer and 400 parts of vinylidene chloride monomer are added to the reactor instead of the 370 butadiene monomer/630 parts vinyl- "idene chloride monomer used in Example 1 and the polymerization is allowed to proceed until a copolymer of 40:60 vinylidene chloride: butadiene is obtained. The

-'test results which are obtained are tabulated in Table EXAMPLE VI The procedure of Example 1 is repeated except that the width of the annular orifice of the die at the end of the extruder is changed from 0.20 inch to 0.35 inch to produce aplastic bottle having approximately 0.060 inch average body wall thickness. All other conditions are the same as set forth in Example 1 and the results of the tests are tabulated in Table 1.

TABLE I TEST EXAMPLES 1. Polymer Processability i.e., acceptable (A) not acceptable 2. Oxygen Permeability (cc/day/lOO sq. inJmiI-atm. at 73 F.) 1

3. Water Permeability (gm/day! 100 sq. inJmil at 73F.-

percent RH) 4. Toughness EMFH at 73F. (feet) 5. Product Absorption Loss) Water Vapor Permeability (grams/day/IOO sq. in./mi1 at 100F. l percent RH) 7. Stiffness (Modulus-psi) 8. Heat Distortion Temperature 9. Product Ingredient lmpermeability a. Polar Liquid Permeabi1ity(grams)/ day/ sq.in./mi1 at 73F.-50 percent RH) b. Non-polar Liquid Permeability grams/day/ 1 00 sq.in./mil at 73F.

50 percent RH) Density (grams/cc at 73F.)

Steam Sterilizability Acceptable (A) Not acceptable (N) 7 As is apparent from Table I, significant variations in property levels are'obtained depending on the proportion of vinylidene chloride to butadiene in the interpolymers. More specifically, with respect to Polymer Processability (Item I) a very poor result is obtained when the proportionof vinylidene chloride is 85 parts to 15 partsbutadiene, that is, the Polymer Processability'of the vinylidene chlo'ridezbutadiene interpolymer fallsoff substantially above 70 parts or percent vinylidene chloride. For example, the polymer of Example IV (85:15 vinylidene chloridezbutadiene) could not be processed into a container. Oxygen Permeability (Item 2) also markedly changes when the proportion of vinylidene chloride to butadiene is varied and for packages containing oxygen sensitive products, permeabilities above 7.0 are considered detrimental. As is shown in Table I with respect to Example I, a 5.0 Oxygen Permeability value is recorded for a proportion of 63 parts of vinylidene chloride to 37 parts of butadiene which is toward the lower portion of the critical range. Furthermore, as the Table indicates, oxygen permeabilities of vinylidene chlo'ridezbutadiene interpolymers become increasingly poorer (i.e., above the maximum acceptable value) as the proportion of vinylidene chloride is reduced from the 60 percent lower limit (see test results for Examples III and V). Regarding other properties, Water Permeability (Item 3) should be less than 2 to be effective while Toughness (Item 4) should be greater than or equal to 8 feet. All of the samples tested for Water Permeability were well below the maximum level of 2 while all the samples (except Example IV sample) were acceptable with respect to Toughness.

With respect to Product Absorption (Item 5), the general limit of acceptability for plastics used to package environmental sensitive products is less than or equal to 20 percent. In this'instance, the sample of Example V, wherein the proportion of vinylidene chloride is 40 percent'failed to meet the specification indicating generally that the tendency of the plastic to absorb product ingredients is too high below 60 percent vinylidene chloride. However, the Water Vapor Permeability (Item 6) results are all below 3 which is considered to be the maximum level for-package desirability. Regarding other properties, the Stiffness (Item/7) or modulus (psi) should be greater than 250,000 psi. Examples III and V as shown in the Table indicate that below 60 percent vinylidene chloride the stiffness or modulus falls off significantly below the acceptable value while above 60 percent, the stiffness or modulus is well above the minimum generally acceptable level. Regarding Heat Distortion Temperature (Item 8) all of the samples show distortion temperatures well above the l90F..level which is the minimum generally considered acceptable for the containers of the type described.

above Table I, the results of the samples of Examples III and V indicate poor polar liquid permeabilitiesi With respect to Product Ingredient Permeability (Item 9) the generally acceptable levels for polar liquid permeability and non-polar liquid permeability is less than 5.0 and 25.0, respectively. As can be seen in the Lastly, with respect to Steam'SterilizabiIity (Item I l), the Table shows that the samples containing more than 60 percent vinylidene chloride are acceptable while the samples containing less than 60 percent vinylidene chloride are generally unacceptable.

Sterilizability is not considered acceptable, the oxygen and polar liquid permeabilities are too' high and the stiffness or modulus falls off substantially. Furthermore, below 50 percent vinylidene chloride non-polar permeabilities are too high and the tendency of the plastic to absorb product ingredients is unacceptable. On the other hand, all of the properties considered essential for packaging environmentally sensitive products are acceptable or within acceptable limits when the proportion of vinylidene chloride in the vinylidene chloridezbutadiene interpolymer is within 60 to percent by weight. The molecular weight (Staudinger) of this interpolymer can vary between ZOQOO to 500,000.

As earlier indicated, it is possible to blend the interpolymer of the present invention with up to lOpercent by weight of other polymers or interpolymers and additives which are compatible with vinylidene chloride:- butadiene interpolymers. However, the proportion of other polymers and additives shouldnot be allowed to exceed 10 percent if radical shifts of property levels are to be avoided. Typical polymers or interpolymers which may be blended with the interpolymer of the present invention are polymers prepared from ethylenically unsaturated monomers such as vinyl halide, vinylidene chloride, methyl methacrylate, styrene acrylonitrile, methylstyrene-acrylonitrile, methyl-styrenestyrene-acrylonitrile, butadiene-acrylonitrile, and the like and monomers copolymerizable therewith. Within this I0 percent limitation optional additives such as stabilizers, fillers, colorants, lubricants processing aids and co-plasticizers may also be incorporated such as, methyl methacrylate polymers, styrene-acrylonitrile copolymers, styrene-methyl methacrylate copolymers, epoxy components, chlorinated paraffins and the like.

withstand substantially better than normal handling without rupture or distortion. In addition, the plastic must be shapeable within rather close tolerances. There are many plastics which fulfill these characteristics but do not .on the other hand have the necessary properties as described in Items I thru 11 above. The interpolymer of the present invention will provide containers having wall thicknesses varying anywhere from 0.010 to 0.20 inch not only having the properties referred to above but also structural strength to contain the products under rather rigorous handling conditions. In addition, the interpolymer of the present invention n e haped an me e .tis n ths sn y known molding techniques, i.e., blow molding, vacuum form-; ing and thermoforming. More specifically, the inter polymer can be readily extruded into either a tubularparison which is subsequently blow molded or into a sheet which is subsequently thermoformed by differential pressures or mechanical means. In the former case, the interpolymer is preferably extruded into a tubular parison at a temperature between 400 and 550F. and molded within this temperature range to produce a sharply configured container while in the latter case the sheet is preferably extruded at a temperature between 230 and 380F. and molded within this temperature range to produce a sharply configured container. It is, of course, possible to extrude the preform, i.e., tubular parison, sheet, etc., at a temperature outside the preferred range and subsequently heating the preform to within the preferred molding temperature range.

The polymerization or chemical combining of the vinylidene chloride and butadiene may be carried out by a number of techniques such as mass, solution, emulsion, suspension and even graft techniques. In general, emulsion polymerization is preferred. In the emulsion polymerization process, water, emulsifying agents, and butadiene monomer are charged to an agitated pressure vessel. The vessel is sealed and substantially evacuated of air to substantially eliminate oxygen after which the cold monomer is added and the resulting mixtures agitated at temperatures anywhere between and 45C. Immediately after the first monomer which is preferably the butadiene monomer is completely added to the kettle, the catalyst, i.e., potassium persulfate, lauroylperoxide, acetyl methylcyclo hexane persulfonate, etc., is addedand the polymerization allowed to proceed while adding the other monomer which is preferably the vinylidene chloride monomer until the predetermined copolymer proportions are obg tained. The addition of the second monomer should be very gradual for example, over a 10 to 16 hour period. The remaining monomer after polymerization is vented.

off and the resin recovered by centrifuging, washing and drying.

The amount of water charged to the process is generally adjusted to give maximum vessel productivity consistent with a low slurry viscosity for maintaining adequate heat transfer and storage. As a result, the amount of water charged will generally vary between 100 and 250 parts by weight per 100 parts of total monomer charged. The polymerization may be accelerated by heat, irradiation and polymerization catalysts. Catalysts which have been found to be particularly useful are monomer-soluble organic peroxides which can generally be varied within narrow weight input ranges to obtain polymerization cycles of 10 "to 12 hours or less. Suitable emulsifying agents that can be used to produce the interpolymer are hydrophilic, macromolecular, natural or synthetic colloids and nonionic or ionic synthetic surfactants, and mixtures of the same.

What is claimed is:

1. A bottle for holding environmentally sensitive products having a sidewall thickness of between 0.01 inch and 0.20 inch, said bottle being formed of a plastic comprising an interpolymer of 60 to percent by weight of vinylidene chloride, 40 to 30 percent by weight of butadiene, and 0 to 10 percent by weight of V a polymer compatible with said vinylidene chloride and butadiene, said vinylidene chloride and butadiene cooperating to provide a steam sterilizable bottle with improved toughness as characterized by an EMFH at 73F. of at least 8 feet and improved resistance to oxygen permeability of not more than 7.0 cc/day/ I00 

1. A BOTTLE FOR HOLDING ENVIRONMENTALLY SENSITIVE PRODUCTS HAVING A SIDEWALL THICKNESS OF BETWEEN 0.01 INCH AND 0.02 INCH, SAID BOTTLE BEING FORMED OF A PLASTIC COMPRISING AN INTERPOLYMER OF 60 TO 70 PERCENT BY WEIGHT OF VINYLIDENE CHLORIDE 40 TO 30 PERCENT BY WEIGHT OF BUTADIENE. AND 0 TO 10 PERCENT BY WEIGHT OF A POLYMER COMPATIBLE WITH SAID VINYLIDENE CHLORIDE AND BUTADIENE, SAID VINYLIDENE CHLORIDE AND BUTADIENE COOPERATING TO PROVIDE A STEAM STERILIZABLE BOTTLE WITH IMPROVED TOUGHNESS AS CHARACTERIZED BY AN EMFH AT 73*F, OF AT LEAST 8 FEET AND IMPROVED RESISTANCE TO OXYGEN PERMEABILITY OF NOT MORE THAN 7.0 CC DAY 100 SQ.IN. MIL-ATM. AT 73*F. 